TMDS361B
SLLS988A –SEPTEMBER 2009–REVISED JULY 2011
www.ti.com
OVS
T
RSCL
RSDA
TSCL
TSDA
R
B0344-01
Figure 40. I2C Drivers in the TMDS361B (R Side Is the HDMI Source Side, T Side Is the HDMI Sink Side)
When the T side is driven below 0.4 V by an external I2C driver, both drivers R and T are turned on. Driver R
drives the R side to near 0 V, and driver T is on, but is overridden by the external I2C driver. If driver T is already
on due to a low on the R side, driver R just turns on.
When the T side is released by the external I2C driver, driver T is still on, so the T side is only able to rise to the
VOL of driver T. Driver R turns off, because VOL is above its 0.4-V VIL threshold, releasing the R side. If no
external I2C driver is keeping the R side low, the R side rises, and driver T turns off once the R side rises above
1.5 V; see Figure 41.
Vcc
TSCL/TSDA
0.5V
tPLH
5V +
10%
RSCL/RSDA
Vcc/2
Figure 41. Waveform of Driver T Turning Off
It is important that any external I2C driver on the T side is able to drive the bus below 0.4 V to achieve full
operation. If the T side cannot be driven below 0.4 V, driver R may not recognize and transmit the low value to
the R side.
DDC I2C Behavior
The typical application of the TMDS361B is as a 3×1 switch in a TV connecting up to three HDMI input sources
to an HDMI receiver. The I2C repeater is 5-V tolerant, and no additional circuitry is required to translate between
3.3-V and 5-V bus voltages. In the following example, the system master is running on an R-side I2C-bus while
the slave is connected to a T-side bus. Both buses run at 100 kHz, supporting standard-mode I2C operation.
Master devices can be placed on either bus.
V
VTdd
Rdd
Driver T
Driver R
R
RTup
Rup
Master
Slave
CSOURCE
CI
CO
Cslave
Cmedium
CCABLE
Figure 42. Typical Application
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